One aspect of the invention relates to an improved mixed wire semiconductor lead frame package and a method for producing the package.
Mixed wire semiconductor lead frame packages which include two pluralities of bond wires, each including a different metal, are known. A package 1 of the prior art is illustrated in FIG. 1. The package 1 includes a copper lead frame 2 with a recessed die pad 3 laterally surrounded by a plurality of leadfingers 4 and a semiconductor chip 5 which is mounted to the die pad 3 with die attach material 6. The semiconductor chip 5 includes integrated circuit devices 7 on its upper active surface and a plurality of chip contact pads 8. Some devices are electrically connected to the lead frame 2 by aluminium bond wires 9 and other devices by gold bond wires 10.
Aluminium bond wires 9 of a large diameter are commonly used to electrically connect power devices to the lead frame 2 since a high current capacity is desired. A wedge-bonding technique is commonly used for the aluminium bond wires 9 and a large laterally rectangular bond pad is provided on the chip 5 which increases the chip dimensions. The chip contact pads of devices which require a smaller current capacity are connected to the lead frame by gold wires 10 which typically have a smaller diameter than the aluminium bond wires 9. The gold wires 10 are bonded using a ball bonding technique. Smaller laterally square contact pads are provided on the semiconductor chip 5 for the gold ball bonds.
The aluminium bond wires 9 and gold bond wires 10 are bonded to landing pads 11, 12, respectively, provided on the inner portion of the leadfingers 4. Since a silver-aluminium interface is known to be unreliable, landing pads 11, 12 including two different materials are provided. The landing pads 11 include NiNiP for the aluminium bond wires 9, whereas the landing pads 12 for the gold bond wires 10 include silver, in order that the bond wires 9, 10 form a bond and, therefore, a good electrical connection with the landing pads 11, 12 respectively.
Therefore, in order to manufacture the lead frame 2, which is suitable for the mixed wire semiconductor package 1, the lead frame 2 undergoes two precision electro-plating process steps; one in which the NiNiP landing pads 11 are electroplated and one in which the silver landing pads 12 are electroplated.
The requirement of two precision electroplating process steps leads to high production costs for mixed wire semiconductor packages and the potential risk of cross contamination of the lead frame during the eletroplating of the different metals.